Fluid control system for liquid storage apparatus

ABSTRACT

1,196,065. Liquefied gas storage containers. VEHOC CORP. 16 July, 1968 [21 Aug., 1967], No. 33840/68. Heading F4P. L.N.G. is stored under pressure and near its boiling point in a heat-insulated vessel 20a having no ullage space and vapour evolved due to heat leak together with expanded liquid is vented through a duct 34 leading to a drum 38 of sufficient capacity to accommodate said vented vapour and liquid and having sufficient ullage space to provide for expansion and vaporization due to normal heat leak in the drum itself which latter has a pressure relief vent valve 61 in a discharge stack 62. A plurality of vessels 20a to 20n are vertically mounted in a ship&#39;s hold and have access ducts 21a to 21n connected by relief valve 36a to 36n to the vent duct 34 and by liquid block valves 27a to 27n to an insulated liquid header 26 having one end leading to the drum 38 and the opposite end connectable to a shore liquidfill and emptying line 11 and a pump 12 to a tank 10. The storage vessels have further access ducts 22a connected by relief valves 35a to 35n to vent duct 34 and by block valves 31a to a main uninsulated vapour header 30 connected at one end to drum 38 and connectable at the other end to a shore line 13 and a compressor 14 to the vapour space of tank 10. Vapour block valves 31a-31n are each controlled by a liquid sensor 32a to 32n whilst the liquid block valves 27a to 27n are controlled by vapour sensors 28a to 28n. The liquid level in drum 38 is maintained below a predetermined height by means 49 which withdraws excess liquid, vaporizes it and discharges either through valve 61 and stack 62 or through a line 55 to the ship&#39;s engines or to a burner 59. To fill the vessels 20a-20n and with shore lines 11, 13 connected to headers 26, 30 a valve 48 in header 26 is closed, valves 23a to 23n and open as are valves 15, 16, 29, 33 and pump 12 is operated and liquid flows through open liquid block valves 27a to 27n to the vessels 20a to 20n whilst vapour is forced through open valves 31a to 31n, header 30 and line 13 to tank 10. When a given vessel, say 20a, is filled with liquid, the level reaches a sensor 32a which then closes the liquid block valve 27a, which it controls, and filling is completed when sensor 32n closes valve 27n. During the voyage valves 23a to 23n and 27a to 27n are closed but valve 48 and vapour block valves 31a to 31n remain open whereby expansion liquid in access ducts 22a to 22n gains access to the uninsulated header 30 where it is vaporized and carried through the vent header to the drum 38.

N. H. BERLIN 3,544,289

'FLUID CONTROL SYSTEM FOR LIQUID STORAGE APPARATUS Dec. 1, 1970 Filed Aug. 21, 1967 nmN INVENTOR NORTON H. BERLIN ATTORNEYS 3,544,289 FLUID CONTROL SYSTEM FOR LIQUID STORAGE APPARATUS Norton H. Berlin, Matawan, N.J., assignor to Vehoc Corporation, a corporation of Delaware Filed Aug. 21, 1967, Ser. No. 662,126 Int. Cl. F17b 1/00, 1/14 US. Cl. 48174 18 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION Field of the invention This invention relates to an apparatus and method for storing liquids at or near their boiling point and particularly for containing a natural gas mixture under conditions of pressure and temperature Where the mixture is liquified but begins to vaporize with only minimal addition of heat. Such conditions exist with liquefied natural gas '(LNG) stored at an extremely low cyrogenic temperature and atmospheric pressure, liquefied petroleum gas (LPG) stored at ambient temperature and high pressure, and also with gas mixtures stored under a combination of moderate refrigeration and pressure near the bubble point (MLG) as described in United States Patent No. 3,298,805. Applications to fluids other than natural hydrocarbons, such as liquefied oxygen or carbon dioxide, will become apparent from the following description.

In large-scale storage (whether for shipment or for static containment) of virtually all liquefied materials substantially at the boiling point, safeguarding measures are necessary to control the stored fluid in the event of expansion and vaporization. Some expansion of the contained liquid is inevitable during containment due to heat leak into the material and it must be accommodated without undue pressure increases. Also, a certain amount of boiling of the contained liquid can occur over a period of time, Whether it be from heat transfer into the system, a pressure drop due to inadvertent leakage, or accidental causes such as pipe breakage or failure of a thermal barrier. When this happens vapor is evolved from the stored liquid and unless it is properly handled it can produce dangerous pressure increases or chilling effects or both. Rupture of the containers can occur and in some instances, such as in the shipboard transportation of flammable natural gas mixtures, loss of life and property is not unlikely.

The specific purpose of the present invention is the safe and economical control of liquid expansion and vapor evolution generated from a liquid during its containment at or near the boiling point.

Description of the prior art Since the present invention was developed especially for application to the transportation of natural gas mixtures, that is the area where the known prior art of significance is found. Conventional methods of transporting liquefied natural gas, or LNG as it is described above, and liquefied petroleum gas, or LPG as it is described above, have produced essentially one fluid control concept which can be called the ullage technique. On board United States Patent ice ship, for example, the liquid cargo is loaded into a plurality of vessels connected by headers but every vessel is only partially filled for the voyage. In each of them a sizeable pocket of vapor, or ullage," is left in the upper region of the vessel and its principal function is to accommodate at least the unavoidable liquid expansion caused by heat leak and insure that no liquid (only vapor) reaches the relief values at the upper end of the vessel. If liquid were to escape through the relief valves, it would flash or spill and cause a severe hazard to personnel and equipment. The ullage pocket thus insures that only vapor is expelled from the vessels and it can be safely disposed of by venting, chilling or burning.

The disadvantages of the techniques which involve ullage in each storage vessel are not that they inadequately protect against liquid expansion or uncontrolled vaporization but rather that they are inseparable from certain highly undesirable side effects. For one thing they entail an inefficient use of the container volume which is available since none of the containers is completely filled with the liquid. A significant percent by volume of the storage capacity of an LNG ship is normally reserved for ullage, which-is to say occupied by a vapor phase of the natural gas cargo which is far less dense than the liquid phase. Also a storage vessel designed for ullage must be equipped not only with liquid and vapor access conduits but also a third access conduit for disposing of liquid in excess of the safe level. Another shortcoming is that ullage presupposes an interface of liquid and vapor in each vessel and being of different densities they undergo changes of inertia differently. As a consequence the liquid sloshes about in the vessel when the vessel accelerates not only complicating the operation of the ship and the structural design of the vessels and their supports but adding to the tendency of the liquid to vaporize at its surface.

SUMMARY OF THE INVENTION The invention is applicable to fluid storage apparatus wherein a liquid is contained substantially at its boiling point in vessel means which are loaded and unloaded through liquid and vapor headers connected thereto. In

' particular the invention provides a safety system for controlling liquid expansion and vapor evolution during containment without necessitating ullage in the vessel means. The system comprises a vent header connected to the vessel means, and block valve means for closing off the vessel means from the liquid header during containment. A fluid control drum is included with which both the vent and vapor headers are connected for receiving and separating liquid and vapor expelled from the vessel means due to expansion or vaporization or both. This drum is of a capacity at least sufiicient to contain ullage plus the total liquid expansion produced in the vessel means from normal heat leak. Fluid in excess of a given pressure is removed from the drum by Withdrawal means. In order to control the transfer of fluid from the vessel means into the drum, relief means are included which comprise (i) pressure control valve means for directing through the vapor header whatever vapor evolution and liquid expansion results from normal heat leak and (ii) relief valve means for directing through the vent header whatever additional volume of vapor or liquid may be generated due to abnormal causes.

The vessel means are usually a plurality of individual vessels, perhaps interconnected in parallel to form banks which in turn are connected in parallel by the headers. All of the vessels can be completely filled with the liquid cargo in accordance with the invention, so that there is no sloshing even when the vessels are subjected to inertial changes on board ship. Only two access conduits are required for each vessel, one for vapor and the other for liquid. As to utilization of the available storage space in the vessels, the safety system of the invention is far more efficient than known techniques employing ullage in each vessel. Only one ullage pocket is relied on in the present invention and that is in the fluid control drum. Any vessel undergoing vaporization or liquid expansion is immediately in communication with the drum through either the vapor header or the vent header. While the drum is large enough to accommodate safely the maximum liquid expansion from a number of vessels and still have the requisite ullage, if nonetheless embodies far less of an allocation of nonusable storage space as compared to providing ullage in each bottle.

For example, a conventional vessel may require onehalf percent of its capacity as ullage against the maximum inevitable expansion of the liquid due to heat leak during containment. Another two percent may then be set aside as an additional margin of safety to insure that the liquid level never reaches the vapor relief valve at the top of the vessel. Hence, two and one-half percent of the total vessel capacity of the ship is devoted to ullage. According to the present invention all the vessels on the ship would be filled with liquid and only the fluid control drum would contain ullage. The drum would be large enough to hold (a) all of the expanded liquid likely to come from the bottles due to heat leak and this is one-half percent of the total vessel volume in the example, and (b) two percent of its own volume set aside as ullage to protect its own vapor relief valves from the liquid level. Only two percent of one-half percent (i.e., one one-hundredeth of a percent) of the total vessel capacity of the ship would then be devoted to ullage per se.

BRIEF DESCRIPTION OF THE DRAWING The drawings is a schematic representation, partly broken away, of an arrangement of storage vessels on board a ship in relation to certain shore facilities and also to the vapor control system of the invention.

DESCRIPTION OF A PREFERRED EMBODIMENT The broken line L in the drawing signifies the division between the shore facilities and the apparatus on board ship to which the invention relates. The subject matter shown to the right of the line L is part of the shore facilities, and it includes a large capacity storage tank which serves as a reservoir from which the cargo fluid is taken during loading and into which it is deposited during unloading of the ship.

The cargo fluid in this example is a natural gas mixture containing at least 60 mol percent methane and at least 80 mol percent methane-plus-ethane, the remainder being heavier hydrocarbons and up to 10 mol percent inert constituents. Such a mixture has a gross calorific value of from 800 B.t.u./s.c.f. to 1600 B.t.u./s.c.f. During the voyage on shipboard, the mixture is to be contained in the liquid state at a temperature between about 116 F. and 200 F., and at a pressure at or immediately below the bubble point-dew point pressure at the chosen operating temperature. Under these operating conditions, the mixture is substantially in its equilibrium state where vaporization occurs on the surface of the liquid as a result of the addition of only a small amount of heat. For a natural gas mixture having a mol percent composition of 88.80 percent methane, 5.02 percent ethane, 2.71 percent propane, 2.43 percent butane, .03 percent pentane, .01 percent hexane, .34 percent nitrogen and .66 percent carbon dioxide (with a specific gravin which there is a compressor 14. Valves and 16 are located in the conduits 11 and 13 respectively.

On board the ship there is a multiplicity of pressure vessels arranged in banks 20a to 2011. In a typical application there may be about three hundred vessels on a given ship. The vessels vary in size depending upon where they are located in the ship, perhaps in a range from 15 to 60 feet in length with a diameter of about 10 feet. They are vertically disposed in the hold of the ship in compartments which are lined with thermal insulation to prevent substantial heat leakage into the cargo. The vessels are made of a suitable alloy resistant to the compression and refrigeration necessary to keep the cargo mixture in the operating state described previously. Each vessel is fully closed except for liquid and vapor access conduits 21a to 21n and 22a to 22n respectively which extend through the respective upper ends of the vessels and communicate with the bottom and top regions respectively of the interior thereof. Unit valves 23a to 2321 are provided in the respective liquid access conduits 21a to 2111 and can be opened or closed by a switch on a remote control panel on the ship.

In each of the respective banks of vessels, liquid subheaders 24a to 24n connect the respective liquid access conduits 21a to 21n in parallel and vapor subheaders 25a to 25n connect the respective vapor access conduits 22a to 22n in parallel. The liquid and vapor subheaders may be disposed substantially laterally in the ship over the tops of the vessels in a sealed-off tween deck area which may be considerably warmer than the hold containing the vessels. All of the vapor and liquid subheaders are preferably surrounded by jackets of thermal insulation.

The system also includes a liquid header 26 extending longitudinally in the ship in the tween deck area and it is also surrounded by a jacket of thermal insulation. The

. liquid header 26 interconnects all of the liquid subheaders ity relative to air of .648), the contemplated operating 24a to 2412. Liquid block valves 27a to 27n are located at the respective interconnections between the liquid header 26 and the liquid subheaders 24a to 2411. On the vessel side of each of these liquid block valves 27a to 2711 is a respective vapor sensor 28a to 28n which recognizes the arrival of an interface of liquid and vapor at that point and initiates certain operations which are described below. A valve 29 is located in the liquid header 26 in a position to control flow of fluids to and from the conduit 11 when the ship is linked to the shore facilities during loading and unloading.

Avapor header 30 also extends longitudinally in the ship in the tween deck area and it is not thermally insulated. This vapor header 30 is connected to the respective vapor subheaders 25a to 2511. At the respective intercon nections between the vapor header 30 and the vapor subheaders 25a to 2521 are corresponding vapor block valves 31a to 3111. To the vessel side of each of these vapor block valves is an associated liquid sensor 32a to 32m which recognizes the arrival of a liquid vapor interface for purposes described below. A valve 33 is located in the vapor header 30 to control flow to and from the conduit 13 when the ship is linked to shore facilities during loading and unloading.

The safety system of the invention includes a vent header 34 extending longitudinally in the ship and connected to each of the vapor subheaders 25a through 25n. which includes respective vapor relief valves 35a to 35n. The vent header 34 is also connected to the respective liquid subheaders 24a to 2411 through liquid relief valves 36a to 36n. The vent header 34 communicates directly with a fluid control drum 38 which is perhaps slightly larger in volumetric capacity than any one of the vessels 20a to 2011 but not substantially so. The matter of its size is discussed hereinafter. The drum 38 may conveniently be located in the forward part of the ship.

The vapor header 30 is also connected to the drum.

drum drops below a given level. A conduit 41, 41 permits circumvention of the downstream pressure control valve 40 by fluids flowing from the vapor header 30. An upstream pressure control valve 42 is located in the con duit 41 to convey fluids from the vapor header 30 into the drum 38 around the downstream pressure control valve 40 when the pressure in the vapor header 30 rises above a predetermined level. The vapor header 30 is also connected to the vent header 34 through a connection 43 in which a safety valve 44 is located. In like manner, the liquid header 26 is connected to the vent header 34 through a connection 45 in which a safety valve 46 is located. Finally a bypass 47 joins the liquid header 26 with the conduits 41, 41' and it contains a valve 48 which is operable from a remote control panel.

In a typical installation, the vent header 34 may be the largest in diameter, followed in order by the liquid header 26, the vapor header 30, the vapor subheaders 25a to 25n, and the liquid subheaders 24a to 24n.

Level control means 49 are provided for converting liquid in excess of a given volume to vapor in the drum 38 by the addition of heat. This consists of a transfer conduit 50 into which the liquid passes through a sea water heater 51 which is operated by a control 52 in response to the level of liquid in the knockout drum 38. Whenthe liquid level in the drum 38 exceeds a given point, the level control means operates to withdraw and vaporize some of the liquid to return the vapor to the drum 38.

Withdrawal means are provided for removing vapor from the drum 38. This includes a vent conduit 54 from which the vapor may proceed through a conduit 55 into a fuel heater 56 and thence to the ships engines 57 for consumption as a primary propulsion energy source. Alternatively, vapor may proceed from the vent conduit 54 through a conduit 58 to a burner 59 where it is ignited in heat exchange relation with sea water with the products of combustion expelled through a fiue 60. Finally, vapors may proceed from the vent conduit 54 through an ultimate relief valve 61 and thence to a stack 62 opening to the atmosphere.

The operation of this apparatus is as follows:

When the ship is ready for loading at dockside its bank of vessels 20a through 20n may be at approximately the contemplated operating temperature (about 170 F.) and are filled with vapor. The liquid and vapor headers 26 and 30 are connected to the respective conduits 11 and 13 by a suitable ship-to-shore linkage. The valve 48 is closed and the unit valves 23a to 23n are opened. Upon opening of the valves 15, 16, 29 and 33, the pump 12 is operated and liquid from the storage tank flows into the ship through the liquid header 26. It proceeds through the open liquid block valves-27a to 2711 and the liquid subheaders 24a to 2411 into the lower regions of the respective pressure vessels a to 20n. As the vessels fill with liquid, vapor passes out through the open vapor block valves 31a to 31n, through the vapor header to shore, and from the conduit 13 back into the storage tank 10. When a given bank of pressure vessels such as 20a fills with the liquid, the liquid level reaches the liquid sensor 32a as a result of which the liquid block valve 27a in that bank is caused to close. This may be completed in various banks throughout the ship at various times due to differences in capacity. If desired, successive groups of banks may be filled in turn, such as filling one quadrant of the ship after another. During the voyage, theunit valves 23a to 23H on the respective vessels are closed, as are the liquid block valves 27a to 27n, but the vapor block valves 31a to 31n are left open. The valve 48 is also opened when the voyage commences so that the liquid intentionally left in the liquid header 26 will have access to the vapor header 30 through the bypass 41. It will be noted that the liquid header 26, which is surrounded by thermal insulation, is filled with liquid cargo throughout the voyage and may be the equal in capacity to about six additional pressure vessels.

As soon as the liquid cargo had entered the ship during loading and throughout its containment in the course of the voyage, there is an inevitable leakage of heat into the contained cargo which causes the liquid to expand and in some instances to vaporize. The safe control of this expansion and vaporization, which is the object of the invention, is the same in any one given bank of vessels and hence it will be described with reference to the bank of vessels 20a.

The unit valve 23a is closed on each of the vessels in the bank so that the liquid expansion due to heat leak raises the liquid level in the vapor subheader 25a through the open vapor block valve 31a toward the vapor header 30. Since this is in the warm tween deck area the rising liquid will vaporize and the evolved vapor will be carried through the vent header 34. Normally the ships engines will be consuming this vapor by withdrawing it from the drum 38. Whenever the engines 57 consume so much fuel that the pressure drops in the drum 38 below a certain point, the downstream pressure control valve 40 opens and allows more vapor to enter the knockout drum from the vapor header 30. The vapor header 30 is not insulated and hence any droplets of liquid entrapped therein tend to be heated and vaporize, but if any liquid is carried along into the drum 38 it settles in the lower region thereof. However, the drum 38 is large enough so that if all of the vessels 20a to 20n expelled their full amount of likely liquid expansion through the vent header 34 and none of it vaporized, there would still be a safe amount of ullage in the drum 38 to keep the liquid away from the conduit 55 and ultimate relief valve 61.

As an added safeguard, whenever too much liquid collects in the drum 38, the level control means 49 immediately limits it by converting part of the liquid to vapor. If the engines 57 are closed down or idling, their fuel consumption drops and the pressure in the drum 38 will go up. No vapor would be flowing through the downstream pressure control valve 40 under those circumstances. However, if the pressure in the vapor header 30 becomes too great, the upstream pressure control valve 42 will open to allow the excess vapor to be conveyed through the conduits 41, 41 and on into the drum 38. Excess pressure in the drum 38 is relieved either by consumption of vapor in the burner 59 or by automatic opening of the ultimate relief valve 61 which vents the excess vapor to the atmosphere. Use of the burner 59 is preferred when the ship is in port and the engines are not consuming evolved vapor, since it would be inadvisable under those circumstances to contaminate the atmosphere by discharge through the stack 62.

In addition to handling the limited amount of liquid expansion and vapor evolution due to normal heat leakage the safety system of the invention is also designed to handle whatever further vapor may be flashed oif due to abnormal causes. For example, if sea water flooded around a bank of vessels in the ship, their temperature would rise immediately and there would be considerable expansion and vaporization of their liquid contents. This would cause ,the vapor relief valve 35a to open and immediately carry off the evolved vapor through the vent header 34 to the drum 38. All vapor block valves 31a to 3111 would be closed automatically under these emergency conditions except in the affected bank or banks of vessels. If liquid in large quantity enters the drum, its level is controlled by the control means 49. The excess vapor in the drum may have tqbe withdrawn not only by the engines 57 and the burner 59, but by the stack 62 as well. The function of the vent header 34, therefore, is to provide a direct large-capacity flow path for any or all of the vessels 20a to 20n to the drum 38 under emergency conditions.

An instance when the vapor header would be used in an emergency is in the event of rupture of one of the vapor access conduits 22a to 22n, the most likely point of failure. If that were to occur, the entire aflected bank would be vented through the vapor header 34 to reduce leakage into the tween deck area.

Other safety features are the provision of the valves 44 and 46. The safety valve 44 permits flow from the vapor header 30 to the vent header 34 and thence to the knockout drum 38, in the event the pressure control valves 40 and 42 fail to open. The safety valve 46 permits the contents of the liquid header 26 to be relieved into the vent header 34 through the connection 45 for precisely the same reasons that the individual vapor relief valves 36a to 36n are provided in association with the individual banks of vessels.

When the ship is to be unloaded, the liquid and vapor headers 26 and 30 are linked to the conduits 11 and 13 and the valves 15, 16, 29 and 33 are opened. The valve 48 is closed, all of the unit valves 23a to 2311 are then opened, and the compressor 14 is operated to prime the system and the compressor 14 and the pump 12 together force the cargo liquid out through the liquid header 26 and into the storage tank 10. Again, this may be done in quadrants if desired. When a given bank such as the vessels 20a is emptied, a vapor interface arrives at the vapor sensor 28a which causes the liquid block valve 27a to close and isolate the emptied bank.

I claim:

1. In fluid storage apparatus wherein a liquid is contained substantially at its boiling point in vessel means adapted for loading and unloading by means of liquid 8. Apparatus according to claim 1 wherein means are provided for communicating said vapor header directly with said vent header in the event pressure in the vapor header becomes excessive.

9. Apparatus according to claim 1 wherein means are provided for communicating said liquid header directly with said vent header in the event pressure in the liquid header becomes excessive.

10. In apparatus for transporting a natural gas hydrocarbon mixture by ship wherein the liquefied mixture is contained under compression and refrigeration substantially at its boiling point in thermally insulated banks of parallel-connected pressure vessels which are loaded and unloaded by means of liquid and vapor headers connected in series to the banks of vessels, said liquefied mixture substantially completely filling each of said pressure vessels, a safety system for controlling liquid expansion and vapor evolution during containment.withoutnecessitating ullage in the vessels comprising and vapor headers connected thereto, said liquid substantially completely filling said vessel means, a safety system for controlling liquid expansion and vapor evolution during containment without necessitating ullage in the vessel means comprising (a) a vent header connected to said vessel means; (b) block valve means for closing off said vessel means from said liquid header during containment;

(c) a fluid control drum with which both said vent and I vapor headers are connected for receiving and separating liquid and vapor expelled from said vessel means from said liquid header during containment; drum being of a capacity at least suflicient to contain ullage plus the total liquid expansion produced in said vessel means from normal heat leak; (d) withdrawal means for removing fluid from said drum in excess of a given pressure; and (e) relief means for controlling the transfer-of fluid from said vessel means into said drum comprising (i) pressure control, valve means for. directing through the vapor header whatever vapor evolution and liquid expansion results from normal heat leak, and

(ii) relief valve means for directing through the vent header whatever additional volume of vapor or liquid may be generated due .to abnormal causes.

2. Apparatus according to claim 1 wherein said vessel means comprises a plurality of vessels to which said headers are connected in series..

3. Apparatus according to claim 1 wherein said vessel means comprises banks of parallel-connected vessels, said banks being connected in series by said headers.

4. Apparatus according to claim 1 wherein said fluid is a natural gas hydrocarbon mixture contained in said vessel means under compression and refrigeration.

5. Apparatus according to claim 1 wherein level control means are included for automatically disposing of liquid in excess of a given volume in said drum.

6. Apparatus according to claim 5 wherein said level control means vaporizes excess liquid from the drum arid returns the vapor to the drum.

7. Apparatus according to claim 1 wherein said withdrawal means include means for both consuming and venting excess vapor from the drum.

.posal means comprises combustion means for burning the (a) a vent header connected in series to the banks of vessels;

- (b) block valves for closing 01f each bank of vessels from the liquid header during containment;

(c) a fluid. control drum with which both said vent and vapor headers are connected for receiving and separating liquid and vapor expelled from said vessel means due to expansion or vaporization or both, the capacity of said drum being at least suflicient to contain ullage plus the total liquid expansion produced I in said vessels from normal heat leak;

(d) level control means for converting liquid in excess of a given volume to vapor in said drum by the addition of heat;

(e) withdrawal means for removing fluid from said drum in excess of a given pressure comprising (i) fueling means for withdrawing vapor as a fuel supply for the ship, (ii) disposal means for withdrawing all vapor in excess of said fuel supply; (f) relief means. for controlling. the transfer of fluid from said vessels into said drum comprising (i). a pressure control valve in the vapor header for directing therethrough at least enough vapor to supply fuel for the ship plus whatever additional vapor evolution and liquid expansion results from normal heat leak, and (ii) relief valves'between the vent header and each bank of vessels for directing through the vent headerwhatever additional volume of vapor or a liquid may be generateddue to abnormal causes. 11. Apparatus according to claim 10 wherein means are provided for communicating said vapor header directlywith said vent header in the event pressure in the vapor header becomes excessive.

12. Apparatus according to claim 10 wherein means are provided forcommunicating said liquid header directly .with said vent header in the event pressure in the liquid header becomes excessive.

. 13. Apparatus according to claim 12 wherein said liquid header is thermally insulated and filled with liquid during containment in the same manner as said vessels.

14. Apparatus according to claim 10 wherein said vapor header is free of thermal insulation to promote vaporization of liquidtherein. r I

15.. Apparatus according to c1aim 10 wherein saiddisexcess vapor in heat exchange relation with sea water and also stack means open to the atmosphere for venting whatever. excess vapor cannot be burned or consumed as fuel.

16. A method for controlling liquid expansion and vapor evolution during containment in vessel means ofa liquid substantially at its boiling point without necessitating ullage in the vessel means which comprises 10 (a) substantially completely filling said vessel means withdrawal and vaporization of excess liquid above that with said liquid, level and return of the resulting vapor back to the drum. (b) venting said vessel means of excess liquid or vapor when its internal pressure exceeds a safe level due to References Cited liquid expansion or vapor evolution, 1 5 UNITED STATES PATENTS (c) transferring said excess liquid or vapor to a contro drum large enough in capacity to hold all liquid ex- 322 2231 pansion from said vessel means due to normal heat 3150495 9/196 R d 62 54 leak plus suificient ullage to accommodate the liquid 3232725 2/1966 S 66 ecord et al. 48-190 expanslon WhlCh would occur w1th1n the control 10 3 293 on 12/1966 Lewis et a1 48 190 drum itself due to normal heat leak, and 3,318,104 5/1967 Roszkowski 62 45 (d) relieving said control drum of excess liquid or vapor when its internal pressure exceeds a safe level. MORRIS 0 WOLK, p i Examiner 17. A method according to claim16 wherein the fluid is a natural gas hydrocarbon mixture contained in the 15 SERWINASSIStaHt Exammer vessel means under compression and refrigeration. CL XR 18. A method according to claim 16 wherein liquid in said control drum is kept below a maximum level by 3 54 Dedication 3,544,289.-N0rt0n H. Berlin, Matawan NJ. FLUID CONTROL SYSTEM FOR LIQUID STORAGE APPARATUS. Patent dated Dec. 1, 1970. Dedication filed Sept. 16, 1971, by the assignee, Vehoc Corporation. I Hereby dedicates to the Public the entire remaining term of said patent.

[Oyficial Gazette December 28, 1.971.] 

